Metal wood club

ABSTRACT

A golf club head having indentions provided in a transition zone of the club head. The transition zone of the club head is provided between a first portion of the club head having a first thickness and a second portion of the club head having a second thickness. The indentations are provided at non-structural areas to reduce the weight of the transition zone. The mass can then be moved to a more desirable location in the club head, thereby improving the playability characteristics of the club head, including center of gravity and moment of inertia. The transition zone may be provided at different areas of the club head including the hosel, between the face and the body of the club head and between the crown and sole of the club head. The indentations are provided with the desired height, length and width to achieve weight reduction without effecting the structural integrity of the club head.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 12/760,698, filed Apr. 15, 2010, which is acontinuation-in-part of U.S. patent application Ser. No. 12/404,369,filed Mar. 16, 2009, now U.S. Pat. No. 7,850,543, which is acontinuation of U.S. patent application Ser. No. 12/059,137, filed Mar.31, 2008, now U.S. Pat. No. 7,520,819, which is a continuation of U.S.patent application Ser. No. 11/687,137, filed Mar. 16, 2007, now U.S.Pat. No. 7,361,099, which is a continuation of U.S. patent applicationSer. No. 10/911,341, filed on Aug. 4, 2004, now U.S. Pat. No. 7,207,898,which is a continuation-in-part of U.S. patent application Ser. No.10/428,061, filed on May 1, 2003, now U.S. Pat. No. 7,029,403, which isa continuation-in-part of U.S. patent application Ser. No. 09/551,771,filed Apr. 18, 2000, now U.S. Pat. No. 6,605,007, the disclosures ofwhich are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to an improved golf club head. Moreparticularly, the present invention relates to a golf club head with atransition zone that has a reduced mass, such that the mass can be movedin the club head to provide improved playability characteristics for thegolf club head.

BACKGROUND

The complexities of golf club design are well known. The specificationsfor each component of the club (i.e., the club head, shaft, grip, andsubcomponents thereof) directly impact the performance of the club.Thus, by varying the design specifications, a golf club can be tailoredto have specific performance characteristics.

The design of club heads has long been studied. Among the more prominentconsiderations in club head design are loft, lie, face angle, horizontalface bulge, vertical face roll, center of gravity, inertia, materialselection, and overall head weight. While this basic set of criteria isgenerally the focus of golf club engineering, several other designaspects must also be addressed. The interior design of the club head maybe tailored to achieve particular characteristics, such as the inclusionof hosel or shaft attachment means, perimeter weights on the club head,and fillers within hollow club heads.

Golf club heads must also be strong to withstand the repeated impactsthat occur during collisions between the golf club and the golf ball.The loading that occurs during this transient event can create a peakforce of over 2,000 lbs. Thus, a major challenge is designing the clubface and body to resist permanent deformation or failure by materialyield or fracture. Conventional hollow metal wood drivers made fromtitanium typically have a uniform face thickness exceeding 2.5 mm toensure structural integrity of the club head.

Players generally seek a metal wood driver and golf ball combinationthat delivers maximum distance and landing accuracy. The distance a balltravels after impact is dictated by the magnitude and direction of theball's translational velocity and the ball's rotational velocity orspin. Environmental conditions, including atmospheric pressure,humidity, temperature, and wind speed, further influence the ball'sflight. However, these environmental effects are beyond the control ofthe golf equipment manufacturer. Golf ball landing accuracy is driven bya number of factors as well. Some of these factors are attributed toclub head design, such as center of gravity and club face flexibility.

The United States Golf Association (USGA), the governing body for therules of golf in the United States, has specifications for theperformance of golf balls. These performance specifications dictate thesize and weight of a conforming golf ball. One USGA rule limits the golfball's initial velocity after a prescribed impact to 250 feet per second±2% (or 255 feet per second maximum initial velocity). To achievegreater golf ball travel distance, ball velocity after impact and thecoefficient of restitution of the ball-club impact must be maximizedwhile remaining within this rule.

Generally, golf ball travel distance is a function of the total kineticenergy imparted to the ball during impact with the club head, neglectingenvironmental effects. During impact, kinetic energy is transferred fromthe club and stored as elastic strain energy in the club head and asviscoelastic strain energy in the ball. After impact, the stored energyin the ball and in the club is transformed back into kinetic energy inthe form of translational and rotational velocity of the ball, as wellas the club. Since the collision is not perfectly elastic, a portion ofenergy is dissipated in club head vibration and in viscoelasticrelaxation of the ball. Viscoelastic relaxation is a material propertyof the polymeric materials used in all manufactured golf balls.

Viscoelastic relaxation of the ball is a parasitic energy source, whichis dependent upon the rate of deformation. To minimize this effect, therate of deformation must be reduced. This may be accomplished byallowing more club face deformation during impact. Since metallicdeformation may be purely elastic, the strain energy stored in the clubface is returned to the ball after impact thereby increasing the ball'soutbound velocity after impact.

A variety of techniques may be utilized to vary the deformation of theclub face, including uniform face thinning, thinned faces with ribbedstiffeners and varying thickness, among others. These designs shouldhave sufficient structural integrity to withstand repeated impactswithout permanently deforming the club face. In general, conventionalclub heads also exhibit wide variations in initial ball speed afterimpact, depending on the impact location on the face of the club. Hence,there remains a need in the art for a club head that has a larger “sweetzone” or zone of substantially uniform high initial ball speed.

SUMMARY OF THE INVENTION

The present invention relates to a golf club head adapted for attachmentto a shaft. An embodiment of the present invention is a golf club headthat includes a first club portion having a first thickness, a secondclub portion having a second thickness, a transition zone having a massand connecting the first club portion to the second club portion, and atleast two indentations provided in the transition zone. The indentationsreduce the mass of the transition zone. The mass may then be moved to amore desirable location within the club head to improve playabilitycharacteristics such as center of gravity and moment of inertia.

The indentations may be provided on a non-visible portion of the clubhead. Preferably, the club head is hollow and the indentations areprovided on an interior surface of the hollow club head.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention are disclosed in theaccompanying drawings, wherein similar reference characters denotesimilar elements throughout the several views, and wherein:

FIG. 1 is a front view of a striking face of the golf club headdisclosed in the parent patent application; FIGS. 1 a and 1 b arecross-sectional views of the striking face of FIG. 1 taken along lines1A-1A and 1B-1B, respectively; FIG. 1 c is an alternate embodiment fromthe priority patent;

FIG. 2 is a front, exploded view of an alternate embodiment of theparent patent invention;

FIG. 3 is a front plan view of an embodiment of a hitting face of thepresent invention;

FIG. 3A is a cross-sectional view of the hitting face of FIG. 3 takenalong line 3A-3A;

FIG. 3B is an exploded cross-sectional view of the hitting face of FIG.3;

FIG. 4 is a cross-sectional view of an alternate embodiment of a hittingface of the present invention;

FIG. 5 is a cross-sectional view of another alternate embodiment of ahitting face of the present invention;

FIG. 6 is a cross-sectional view of another alternate embodiment of ahitting face of the present invention;

FIG. 7 is a cross-sectional view of another alternate embodiment of ahitting face of the present invention;

FIG. 8 is a cross-sectional view of another alternate embodiment of ahitting face of the present invention;

FIG. 8A is an exploded cross-sectional view of the hitting face of FIG.8;

FIG. 9 is a front exploded view of an alternate embodiment of a clubhead;

FIG. 10 is a perspective view of another alternate embodiment of a clubhead of the present invention;

FIG. 11 is a perspective view of another alternate embodiment of a clubhead of the present invention;

FIG. 12 a is a top perspective view of another alternate embodiment of aclub head of the present invention;

FIG. 12 b is a bottom perspective view of the club head shown in FIG. 12a;

FIG. 13 a is a top perspective view of another alternate embodiment of aclub head of the present invention;

FIG. 13 b is a bottom perspective view of the club head shown in FIG. 13a;

FIG. 14 is a graph of inertance versus frequency for a conventional clubhead;

FIG. 15 is a graph of inertance versus frequency for the inventive clubhead discussed in priority case;

FIG. 16A is a cross sectional view of a prior art transition zone of agolf club head;

FIG. 16B is a cross-sectional view of a transition zone of a golf clubhead according to the present invention;

FIG. 17A is a another cross-sectional view of a portion of a transitionzone of a golf club head according to the present invention;

FIG. 17B is another cross-sectional view of a portion of a transitionzone of a golf club head according to the present invention;

FIG. 18 is a perspective view of the inside of a club head showing anembodiment of the transition zone according to the present invention;

FIG. 19 is a perspective view of the inside of a club head showinganother embodiment of the transition zone according to the presentinvention;

FIG. 20 is a perspective view of the inside of a club head showinganother embodiment of the transition zone according to the presentinvention; and

FIGS. 21A-B are cross-sectional views of the embodiment of thetransition zone of FIG. 20.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Priority U.S. Pat. No. 6,605,007, which has been incorporated herein inits entirety, discloses an improved golf club that also produces arelatively large “sweet zone” or zone of substantially uniform highinitial velocity or high coefficient of restitution (COR).

COR or coefficient of restitution is a measure of collision efficiency.COR is the ratio of the velocity of separation to the velocity ofapproach. In this model, therefore, COR was determined using thefollowing formula:

(v _(club-post) −v _(ball-post))/(v _(ball-pre) −v _(club-pre))

where,

-   -   v_(club-post) represents the velocity of the club after impact;    -   v_(ball-post) represents the velocity of the ball after impact;    -   v_(club-pre) represents the velocity of the club before impact        (a value of zero for USGA COR conditions); and    -   v_(ball-pre) represents the velocity of the ball before impact.

COR, in general, depends on the shape and material properties of thecolliding bodies. A perfectly elastic impact has a COR of one (1.0),indicating that no energy is lost, while a perfectly inelastic orperfectly plastic impact has a COR of zero (0.0), indicating that thecolliding bodies did not separate after impact resulting in a maximumloss of energy. Consequently, high COR values are indicative of greaterball velocity and distance.

As shown in FIGS. 1, 1 a and 1 b, the accuracy of the club and theclub's large zone of uniform high initial velocity are produced byhitting face 2, having central zone 4, a surrounding intermediate zone6, and an optional perimeter zone 8. Preferably, the area of centralzone 4 comprises about 15% to about 60% of the total area of the hittingface 2, and more preferably about 20% to about 50%.

Central zone 4 is comparatively rigid and intermediate zone 6 isrelatively flexible so that upon ball impact, intermediate zone 6 offace 2 deforms to provide high ball velocity, while central zone 4 issubstantially undeformed so that the ball flies on-target. Thus, uponball impact the deformation of intermediate zone 6 allows central zone 4to move into and out of a club head 10 as a unit. Surroundingintermediate zone 6 may be located adjacent to central zone 4, andoptional perimeter zone 8 may be located adjacent to intermediate zone6. As a result, the head exhibits a coefficient of restitution greaterthan about 0.81.

The above is accomplished by providing central zone 4 with a firstflexural stiffness and intermediate zone 6 with a second flexuralstiffness. Flexural stiffness (FS) is defined as each portion's averageelastic modulus (E) times each portion's average thickness (t) cubed or(FS=Et³). The calculation of averages of modulus and thickness is fullydisclosed in the parent application and in the '007 patent, which havealready been incorporated by reference in their entireties. Thedetermination of FS when the thickness varies or when the material isanisotropic is also fully discussed in the parent patent application andin the '007 patent.

Since the flexural stiffness is a function of material and thickness,the following techniques can be used to achieve the substantialdifference between the flexural stiffness of central zone 4 andintermediate zone 6: 1) different materials can be used for eachportion, 2) different thicknesses can be used for each portion, or 3)different materials and thickness can be used for each portion. Forexample, in a preferred embodiment, the thickness of the central zone isgreater than the thickness of the intermediate zone and the material forboth portions is the same.

In club head 10, the above flexural stiffness relationships can beachieved by selecting a certain material with a particular elasticmodulus and varying the thickness of the zones. In another embodiment,the flexural stiffness relationships can be achieved by varying thematerials of the zones with respect to one another so that the zoneshave different elastic moduli and the thickness is changed accordingly.Thus, the thickness of the zones can be the same or different dependingon the elastic modulus of the material of each zone. It is also possibleto obtain the required flexural stiffness ratio through the use ofstructural ribs, reinforcing plates, and thickness parameters. Theparent case application and the grandparent '007 patent describe indetail the preferred ranges of ratios of flexural stiffness betweencentral zone 4 and intermediate zone 6.

Further, as discussed in the '007 patent, two or more differenthomogeneous materials may be used to form hitting face 2. For example,central zone 4 may be of generally uniform thickness and made from astainless steel having a Young's Modulus of 30.0×10⁶ lbs/in². Theadjacent intermediate zone 6 has a continuously tapering thickness fromthe pace perimeter toward central zone 4. The thickness of intermediatezone 6 is defined to change linearly. Intermediate zone 6 is made from atitanium alloy having a Young's Modulus of 16.5×10⁶ lbs/in².Alternatively, as shown in FIG. 1 c, which corresponds to FIG. 10 fromthe '007 patent, central zone 4 may include ribs 4 a made of stainlesssteel having a Young's Modulus of 30.0×10⁶ lbs/in² with a titanium alloyhaving a Young's Modulus of 16.5×10⁶ lbs/in² in the interstitial spaces4 b. Intermediate zone 6 is made from the same titanium alloy. Theflexural stiffness ratio between central zone 4 and intermediate zone 6is calculated in detail in the '007 patent.

Optional perimeter zone 8 preferably increases in thickness compared tointermediate zone 6 to increase the flexural stiffness thereof.Alternatively, optional perimeter zone 8 may increase in flexuralstiffness compared to intermediate zone by forming perimeter zone 8 outof a different material than that of intermediate zone 6. For example,perimeter zone 8 may be made of the same material as central zone 4.Alternatively, perimeter zone 8 may be made of an entirely differentmaterial than that of central zone 4 or intermediate zone 6. Perimeterzone 8 would then be attached to intermediate zone 6, such as bywelding.

Referring now to FIG. 2, which corresponds to FIG. 8 from the parentcase, hitting face 2 may comprise a face insert 42, which is welded ontoa cavity defined on the face. Hitting face 2 may comprise a face insert42 and face support 30. In this embodiment, hitting face 2 is delineatedfrom crown 14, toe 18, sole 22 and heel 32 by parting line 46. Centralzone 4 is preferably disposed on the inner-cavity-facing surface of faceinsert 42, and, as shown, has a generally elliptical shape. Theelliptical central zone 4 is fully disclosed in the parent patentapplication. Central zone 4 is preferably aligned in the direction ofthe low toe to high heel, so that a high COR zone can be established inthe direction of high tow to low heel. This high COR zone advantageouslycoincides with the typical impact patterns created by golfers.

As defined in the parent case, the term “ellipse” or “elliptical” refersto non-circular shapes that have discernable major axis and minor axis,and include, but are not limited to, any quadrilateral shapes,geometrical ellipses, quadrilateral shapes with one or more roundedcorner(s) and unsymmetrical elliptical shapes. The “major axis” isdefined as the axis coinciding with the longest length that can be drawnthrough the non-circular shapes without intersecting the perimeter ofthe shapes at more than two locations, i.e., at the start and end pointsof said length. The “minor axis” is orthogonal to the major axis at ornear its midpoint. As used herein, the term “concentric” refers toshapes that substantially encircle or surround other shapes.

Intermediate zone 6, designated as 6 ₁ and 6 ₂, can be disposedpartially on face insert 42 and partially on face support 30. Atransition zone 7 having variable thickness is disposed between centralzone 4 and intermediate zone 6. Preferably, the thickness of centralzone 4 is reduced to the lesser thickness of intermediate zone 6 withintransition zone 7. This reduces any local stress-strain caused byimpacts with golf balls due to abrupt changes in thickness. Face support30 defines hole 48, which is bordered by rim 49. Face insert 42 can beattached to face support 30 by welding at or around rim 49.

Preferably, face insert 42 is made by milling or stamping and forming.In the manufacturing process, a malleable metal suitable for use as ahitting face, such as titanium, titanium alloy, carbon steel, stainlesssteel, beryllium copper, and other forgeable metals, is heated and thenhammered into the desired shape of the face cup. Examples of someappropriate metals include but are not limited to titanium 6-4 alloy,titanium 15-3-3-3 alloy, titanium 20-4-1 alloy, and DAT 55 and DAT 55G,titanium alloys available from Diado Steel of Tokyo, Japan.

The preferred forging process is die or billet forging, in which apre-measured rod of forgeable metal is heated and placed between a die,which contains the desired shape of face insert 42, and a hammer. Theheated metal is then hammered into the desired shape. An advantage offorging face insert 42 is that the thickness of the face can be as thinas about 0.060 inch (or about 1.5 mm) around the perimeter or edgethereof.

Referring now to FIGS. 3-8, alternate embodiments of hitting face insert42 are shown. In these embodiments, the flexural stiffness of centralzone 4 is higher than the flexural stiffness of intermediate area 6 dueto a dense insert 52 made of a material of greater density than that ofthe material forming the remainder of face insert 42. A cross-sectionalview of a preferred embodiment of the present invention is shown in FIG.3A, wherein face insert 42 includes a plate-like face 50 and an insert52.

Plate-like face 50 is preferably elliptical in shape with a slightlycurved profile, although any shape may be used, such as polygonal,circular or irregular.

The size of plate-like face 50 depends upon the overall size of golfclub head 10. However, in a preferred embodiment, plate-like face 50measures between 80 and 100 mm along the long axis of the ellipse andbetween 35 and 60 mm along the short axis of the ellipse. Morepreferably, plate-like face 50 measures 90 mm along the long axis of theellipse and 50 mm along the short axis. Plate-like face 50 may be ofuniform or non-uniform thickness 53. In one embodiment, thickness 53ranges from 2-5 mm. Preferably, thickness 53 is 2.7 mm graduallytapering to a maximum thickness of 4.5 mm.

Plate-like face 50 preferably includes a cavity 51, shown in theexploded view of FIG. 3B, formed on the surface 55 that faces the innercavity of golf club head 10. Further, in the vicinity of cavity 51,plate-like face 50 preferably increases in thickness, so as to combinethe effects of a thickened central zone as described above with theeffects of the denser material of dense insert 52. In this embodiment,cavity 51 is circular in shape, although the shape of cavity 51 ispreferably chosen to correspond to the cross-sectional shape of denseinsert 52. Although cavity 51 may be made of any size sufficient toaccommodate dense insert 52, in one embodiment, cavity 51 has aninterior width of approximately 14 mm and a depth of approximately 2 mm.

As discussed above, plate-like face 50 is preferably forged, althoughstamping and casting are also suitable manufacturing techniques.Plate-like face 50 may be made of any material discussed herein that issuitable for forming hitting face 2, such as titanium, titanium alloy,carbon steel, stainless steel, beryllium copper. The more preferredmetal is titanium 6-4 alloy, as described above.

Dense insert 52 is shown as being a conical frusta that is relativelysmall in cross-sectional surface area compared to plate-like face 50.Dense insert 52 may take on any shape that is convenient formanufacturing, for example a cylinder or a circular, elliptical orquadrilateral disk. Dense insert 52 is made of a material of greaterdensity than that of plate-like face 50, preferably tungsten orstainless steel, although any material of greater density thanplate-like face 50 is appropriate for use in the present invention,including copper, nickel, and bronze. Dense insert 52 may be milled,stamped from sheet metal, forged, die cut, cast, or made using anytechnique known in the art.

Dense insert 52 is preferably small compared to the size of plate-likeface 50. In the preferred embodiment, dense insert 52 is approximately10 mm in diameter at its widest point and approximately 7 mm in height.As such, dense insert 52 protrudes from surface 55 of plate-like face50, as dense insert 52 is of a greater height than the depth of cavity51. The size of dense insert 52 may be varied so as to control theeffective size of central zone 4.

Dense insert 52 may be directly or indirectly affixed to plate-like face50. In the preferred embodiment, dense insert 52 is contained within acap 56 made of the same material as that used to make plate-like face 50so that cap 56 may be readily welded to plate-like face 50. Dense insert52 may be affixed to an interior surface of cap 56, adhered to at leastone interior surface of cap 56, or simply rest within cap 56. As shown,cap 56 is a conical frusta having an interior cavity shaped so thatdense insert 52 fits tightly within cap 56. Cap 56 may be made using anymethod known in the art, such as casting, stamping or forging.

As such, dense insert 52 is indirectly fixedly attached to plate-likeface 50, in that dense insert 52 is contained within cap 56 which isjoined to plate-like face 50 by a weld bead 58 so that dense insert 52is not dislodged from its position during the repeated impacts ofhitting face 2 with golf balls. Alternately, at least a portion of thecombination of dense insert 52 and cap 56 may be secured within cavity51 using an adhesive, for example hot melt adhesives, epoxy adhesives,polyurethane adhesives, sealants, thermoset adhesives, UV curingadhesives, silicon adhesives, acrylic and cyanoacrylic adhesives.

Referring to FIG. 4, an alternate embodiment of face insert 42 having adense insert 52 is shown. In this embodiment, dense insert 52 is acircular disk that is adhered directly to the inner cavity-facingsurface 55 of plate-like face 50. Alternatively, dense insert 52 mayalso be welded to the surface of plate-like face 50.

Referring to FIG. 5, another alternate embodiment of face insert 42having a dense insert 52 is shown. In this embodiment, plate-like face50 includes a cavity 51 into which dense insert 52 in the shape of acircular disk in inserted. Dense insert 52 may or may not be affixed tothe surface of cavity 51, such as with an adhesive. A flange portion 54extends over dense insert 52 to hold dense insert 52 within cavity 51,i.e., to prevent dense insert 52 from being ejected from cavity 51during repeated impacts with golf balls. Flange portion 54 may be apiece of material welded to plate-like face 50. Alternatively, flangeportion 54 may be formed during manufacturing of plate-like face 50.Face insert 42 is preferably milled and/or stamped. During themanufacturing process, cavity 51 is formed in a thickened central zoneof plate-like face 50. Cavity 51 is formed to a height that is slightlyhigher than the height of dense insert 52. Dense insert 52 is thenpositioned within cavity 51 and preferably adhered to an inner surfaceof cavity 51. The surface of plate-like face 50 is then forcibly struckor hammered to deform the portion cavity 51 protruding over dense insert52, thereby forming flange portion 54.

Referring to FIG. 6, another alternate embodiment of multiple-materialface insert 42 is shown. This embodiment includes a plate-like face 50similar to the plate-like faces of earlier-described embodiments.However, in this embodiment, plate-like face includes a thin-walledcup-like protrusion 60 extending outward from the inner cavity-facingsurface 55 of plate-like face 50. Cup-like protrusion 60 is shown as afrusta, although it may have any shape, such as a hollow cylinder,three-dimensional polygon, or an irregular shape.

Dense insert 52, similar to the dense inserts described above, is sizedand dimensioned to fit tightly within cup-like protrusion 60. Denseinsert 52 may be affixed to the interior of cup-like protrusion 60using, for example, an adhesive. However, dense insert 52 is held withincup-like protrusion 60 by flange portion 54, similar toearlier-discussed flange portions. In this embodiment, however, if thestamping technique is used to form flange portion 54, the excessmaterial comes from the excess height of cup-like protrusion 60.

Referring to FIG. 7, a cross-sectional view of another alternateembodiment of a face insert 42 of the present invention is shown. Inthis embodiment, plate-like face 50 is similar to the plate-like facedescribed above with respect to the preferred embodiment. In thisembodiment, however, cap 56 is a hollow cylinder having an outerdiameter that is less than the diameter of cavity 51. Dense insert 52 isa cylindrical plug that fits tightly within cap 56, preferably affixedtherewithin.

Cap 56 includes a brim 64 that is sized and dimensioned to fit snuglywithin cavity 51. As such, a small amount of clearance exists betweenthe outer diameter of cap 56 and the edge of cavity 51. Weld bead 58 isformed around the edge of cavity 51 and the edge of brim 64 to attachcap 56 to plate-like face 50. This geometry of cap 56 increases thesurface area to which weld bead 58 may affix, thereby increasing thestrength of the joint. As such, the usable life of hitting face 2increases, as the stronger joint is less likely to suffer failure andeject dense insert 52 into the inner cavity of golf club head 10.

Referring now to FIGS. 8 and 8A, yet another alternate embodiment of aface insert 42 of the present invention is shown. In this embodiment,face insert 42 includes plate-like face 50 and a dense insert 52.However, a void 61 is formed at or near the center of plate-like face 50extending entirely through the thickness thereof. Dense insert 52 ispreferably configured such that at least a portion thereof is fittedinto void 61 while a brim portion 63 thereof rests upon or is affixed toa lip or shelf 66 formed in void 61. A flange portion 54, similar tothose flange portions described above, holds dense insert 52 securely inplace. As such, dense insert 52 is visible from the exterior-facingsurface 65 of plate-like face 50. Although the exterior-facing surfaceof dense insert 52 is shown as being substantially flush with surface65, this need not be the case and a gap may exist between the edges ofvoid 61 such that dense insert 52 is still visible.

Example

Inventive Club W is a hollow metal wood club head made generally inaccordance with the embodiment shown in FIG. 7. Club W includes a faceinsert made of a plate of titanium alloy having a tungsten insert weldedto the inner-cavity-facing surface thereof at or near the geometriccenter of the plate. As such, the thickness of Club W varies in that thecentral zone of the face insert is thicker than the perimeter thereof.Club W has a COR measured to be 0.812.

A standard King Cobra® SZ 440 club head is also a hollow metal wood clubhead. The SZ 440 club head has a hitting face having variable thickness.Similar to Club W, the SZ 440 club head is thicker near the geometriccenter of the hitting face and thinner toward the perimeter thereof.However, the thickness variations of the SZ 440 club head hitting faceare manufactured integrally with the hitting face, i.e., the hittingface includes a single plate of material that is machined to remove aportion of the material only around the perimeter of the plate. The SZ440 club head has a COR of 0.814, approximately equal to that of Club W.

Both clubs were tested using the pendulum test, which is the standardtest for club face flexibility or trampoline effect under USGA andinternational rules. This test entails impacting a specific spot golfclub head several times using a small steel pendulum. A characteristictime between the club head and the pendulum is recorded in microseconds(μs), thereby determining the flexibility of the golf club head at thatpoint. In accordance with USGA rules, nine points on the golf club headare so tested. Generally, the longer the characteristic time, thegreater the flexibility of the golf club head.

As shown in Table 1, the characteristic time of the pendulum with Club Wis greater than that of the SZ 440 club face at all tested points. Assuch, the flexibility of Club W is greater than that of the SZ 440 clubface, even though the COR value is approximately the same for both clubheads.

TABLE 1 Nine Point Pendulum Test Results SZ 440, Club W PEN PEN PEN PENPEN PEN PEN PEN PEN High High High Low Low Low Club Model Center ToeHeel Center Toe Heel Center Toe Heel Comparative 235 238 235 229 244 240227 226 232 SZ 440 Inventive Club W 251 269 250 251 266 263 268 255 235

In accordance with another aspect of the present invention, thethickness of intermediate zone 6 or optional perimeter portion 8 onhitting face 2 can be thinly manufactured by removing the weld linesfrom the hitting face to the crown and sole of the club head. Analternate method for improving the performance of hitting face 2 is toremove weld lines and joints of face insert 42 to another surface ofclub head 10. As is known in the art, a weld line or joint is an area ofdiscontinuity, where even if two pieces of the same material are joined,the structural properties of the pieces in the vicinity of the joint arealtered. Removing weld lines to the crown or the sole of a club headallows the thickness of the hitting face to be controlled more preciselyand allows for a thinner overall hitting face. The joints can also beused to alter the properties of the hitting face. In accordance withthis aspect of the invention, the face insert may include one or moreside walls, wherein the side walls may form part of the crown and/orpart of the sole.

Referring to FIG. 9, which corresponds to FIG. 9 from the parent case,face insert 42 comprises central zone 4, transition zone 7, a portion ofintermediate zone 6, partial crown portion 54 and partial sole portion56. Club head 10 correspondingly defines cavity 58 sized and dimensionedto receive face insert 42. Face insert 42 is preferably welded to clubhead 10. Face insert 42 together with face support 30 forms hitting face2. Similar to the embodiment illustrated in FIG. 2, intermediate zone 6,designated as 6 ₁ and 6 ₂, can be disposed partially on face insert 42and partially on face support 30.

Referring now to FIG. 10, another embodiment according to the presentinvention is shown. In this embodiment, central zone 4 of hitting face 2is formed of a face insert 42. Face insert 42 is preferably welded toclub head 10 along weld line 20. Face insert 42 includes a polygonal orelliptical main plate 34 and a sidewall or wing 70 that extends into andforms a part of crown 14. As such, an upper portion 71 of weld line 20is removed to crown 14. As the stress line created by weld line 20 isremoved from hitting face 2, the probability of failure along upperportion 21 due to repeated impact with golf balls is reduced.

Face insert 42 is preferably made from the same material as the rest ofclub head 10, such as titanium, a titanium alloy, steel, or any othermaterial suitable for use as a club head. Face insert 42 is preferablythe same thickness as the rest of club head 10, although face insert 42may be made thicker or thinner in order to affect the flexural stiffnessthereof.

The size and shape of face insert 42 may vary. As stated above,preferably, face insert 42 is a modified oval U-cup or L-cup, but it mayalso be other shapes, such as rectangular, elliptical or circular. Faceinsert 42 preferably forms nearly the entire surface area of hittingface 2. However, face insert 42 may form a much smaller portion ofhitting face. Also, wing 70 may extend into and form a part of sole 22,as shown in FIG. 11, by simply inverting the configuration of faceinsert 42. In this case, the affected weld line is lower weld line 73.

The material properties of face insert 42 can also be affected by themethod chosen to form face insert 42. For example, face insert 42 ispreferably stamped from sheet metal after the metal has been cold rolledor cold worked in order to align the crystal grains of the metal.Stamping metal in this fashion produces a stronger hitting face thanother manufacturing techniques. Further, face insert 42 is thenpositioned within hitting face 2 so that the grain flow pattern of faceinsert 42 runs in a sole-to-crown direction. Alternatively, the grainflow pattern of face insert 42 may run in a heel-to-toe direction or ina diagonal direction. Other methods known in the art may also be used tomanufacture face insert 42, such as forging and casting.

FIGS. 12 a and 12 b show another embodiment of club head 10 similar tothe embodiment shown in FIG. 10. In this embodiment, face insert 42includes a main plate 34, an upper sidewall or wing 70 that extends intoand forms part of crown 14 as well as a lower wing 72 that extends intoand forms part of sole 22. As such, upper weld line 71 and lower weldline 73 are removed to crown 14 and sole 22, respectively, so as toreduce the potential for failure thereof. All other aspects of faceinsert 42 are as described above with respect to FIG. 10.

FIGS. 13 a and 13 b show yet another embodiment of club head 10 similarto the embodiment shown in FIG. 10. In this embodiment, face insert 42includes an upper sidewall or wing 70 that extends into and forms partof crown 14, a lower sidewall or wing 72 that extends into and formspart of sole 22, a heel extension 74, and a toe extension 75. Upper wing70 and lower wing 72 are as described above with respect to FIGS. 10, 12a, and 12 b. Heel extension 74 and toe extension 75 are extensions ofthe main plate of face insert 42 along the horizontal axis 76 thereof ator near the center of the vertical axis 78 thereof. This alteration ofthe geometry of face insert increases the deflection capabilities offace insert 42 along horizontal axis 76 while vertical axis 78 has adifferent, lesser deflection capability.

Face insert 42 is preferably of a size and general shape as describedabove with respect to the embodiment shown in FIGS. 10, 12 a and 12 b,i.e., a polygonal or elliptical main plate that forms much of thesurface area of hitting face 2. Upper wing 70 and lower wing 73 arepreferably generally elliptical or polygonal, although other shapes arecontemplated by the present invention. Similarly, heel extension 74 andtoe extension 75 are preferably semi-elliptical in shape, although othershapes such as semi-circular are contemplated by the present invention.As such, the preferred geometry of face insert 42 is a central ovalhaving a long axis along horizontal axis 76 of hitting face 2 andgenerally rectangular extensions stretching along vertical axis 78 ofhitting face 2. Further, one of heel extension 74 and toe extension 75may be eliminated. Also, one or both of upper wing 70 and lower wing 73may be eliminated. Further, face insert 42 may incorporate a denseinsert as shown in any of the embodiments shown in FIGS. 3-8 forincreased performance effects. Face insert 42 may also contain centralzone 4 and intermediate zone 6, where the flexural stiffness of centralzone 4 is higher then the flexural stiffness of intermediate zone 6, asdescribed above and as described in the parent application and in thegrandparent '007 patent. Additionally, central zone 4 may also include adense insert 52 as described above.

Hitting face 2 is preferably milled or stamped and milled. The body ofclub 10 is preferably cast. The inner cavity of club head 10 may beempty, or alternatively may be filled with foam or other low specificgravity material. It is preferred that the inner cavity has a volumegreater than 250 cubic centimeters, and more preferably greater than 275cubic centimeters, and most preferably 350 cubic centimeters or more.Preferably, the mass of the inventive club head is greater than 150grams but less than 220 grams. Further part and manufacturing detailsand additional test results regarding the COR values of inventive clubheads are discussed in detail in the parent case.

Yet another parameter that reflects the stiffness of a structure isinertance. Generally, inertance is a frequency response. Morespecifically, inertance reflects the stiffness of a structure, in thisinstance the club face, at various frequencies of vibration. The unitsof inertance are acceleration units over force units. A preferred firstresonant frequency for the inventive club face described herein islocated where inertance is maximized. The testing methodology andapparatus for determining inertance are described in further detail inthe parent patent, U.S. Pat. No. 6,605,007, which patent is incorporatedherein in its entirety by reference.

Referring to FIG. 14, a graph of inertance versus frequency for aconventional club head is shown. The conventional club head is aCallaway Great Big Bertha War Bird with an eight degree loft. The pointI1 at a frequency of 3330 Hertz represents the first primary resonantfrequency which occurs at the first primary maxima inertance for theinertance function I. A maxima which does not represent a primaryresonant natural frequency of the face is also present in FIG. 14 at afrequency of 2572 Hertz, which is designated as point 12. Thesesecondary maxima 12 are characterized by inertance transitions of amagnitude of less than 10 decibels. These secondary maxima may be due tocrown, sole or skirt vibrations that are not acting perpendicular to theplane of the club face. Secondary maxima do not correlate with COR andball velocity, since the vibration response is either small in magnitudeor alternately not coincident with ball response. The COR for theconvention club head tested was measured in accordance with USGA, Rule4-1e Appendix II Revision 2 dated Feb. 8, 1999 and was found to be0.785. The preferred first primary resonant frequency of vibration isdefined by the following relationship:

1/(2*contact duration)<I1<3/(2*contact duration)

The contact duration is the time interval during which the ball is incontact with the club face. The contact duration for a typical driverimpact is about 500 microseconds. Thus, the preferred primary resonantfrequency of vibration for the conventional club head is between about1000 and 3000 Hertz. The closer the COR is to the lower limit, thehigher the COR and thus the higher the rebound ball velocity. Morepreferably, the first primary resonant frequency is less than 2900.

FIG. 15 illustrates the inertance function of the inventive club headdescribed and claimed in priority U.S. Pat. No. 6,605,007 (“the '007club”). The first primary resonant frequency of vibration for the clubhead is at 2632 Hertz, and the COR of the '007 club was measured to be0.824. The COR of the '007 club was measured to be 0.824. The COR of the'007 club is greater than the conventional club of FIG. 14, andtherefore will provide greater ball rebound velocity.

The overall flexural stiffness of a club head and the distribution ofthe flexural stiffness across the face of the club head impact theresonant frequency of a club head. Furthermore, the swing speed willdetermine if the club and/or a golf ball vibrates at the resonantfrequency upon impact. As such, by altering the structural design andproperties of a club head, a club designer may alter the resonantfrequency of the club head to coordinate with the resonant frequency ofa particular golf ball so as to maximize the distance traveled by theball when struck at a certain swing speed. Also, if the club is designedwith a particular golfer in mind, the club can be designed to resonateupon striking a particular golf ball at the golfer's average swingspeed. For example, if the club and the ball resonate at a similarfrequency, if they strike each other so as to produce resonance, thenthe vibrations of both club and ball act to push the ball off of theclub face faster. Preferably, the resonance frequency of the club is0-20% greater than the resonant frequency of the ball. More preferably,the resonance frequency of the club is 0-10% greater than the resonantfrequency of the ball.

A portion 100 of a club head 101 is shown in FIG. 16A, the portion 100includes a first portion 102 have a first thickness t₁ and a secondportion 103 having a second thickness t₂. A transition zone 104 connectsthe first and second portions. Preferably, the first thickness t₁ doesnot equal the second thickness t₂. The transition zone 104 generally hasadditional mass or material that is not needed for structural integrityof the club head 101. The transition zone 104 generally has anon-uniform thickness as the club head transitions from the firstportion 102 having the first thickness t₁ to the second portion 103having the second thickness t₂. As shown in FIG. 16B, according to theinvention, an indentation or scallop 105 is included in the transitionzone 104. The indentation or scallop 105 removes some of the material inthe transition zone 104. The removal of material reduces the weight ofthe transition zone. This mass may then be moved to desired areas of theclub head, such as low and/or back in the club head to improve theplayability characteristics of the club head, including center ofgravity and the moment of inertia of the club head. Preferably, thecenter of gravity is moved at least 0.5 mm lower in the club head, 0.5mm back in the club head or both. For example, the center of gravity maybe moved below a horizontal center line of the club head by at least 1mm. One or more of these indentations or scallops 105 may be placedwithin one or more transition zones 104 of the club head. Theindentations 105 do not appreciably effect the structural integrity anddo not create stress risers or concentrations in the transition zones104. The indentations 105 of the transition zones 104 of FIGS. 16-21 maybe combined with a club head having any type of strike face. Moreover,the indentations 105 of the transition zones 104 of FIGS. 16-21 may becombined with the improved striking faces disclosed in FIGS. 1-13 b.

The transition zones 104 may be found in any portion of the club head101 with a thickness transition from a first thickness t₁ to a secondthickness t₂. Some transition zones 104 of club heads are particularlysuited to having indentations 105 for weight reduction, these includebetween the face and body of the club head, between the crown and skirtand the skirt and sole of the club head and on the hosel of the clubhead. A transition zone 104 may also be found in the hosel of the clubhead. Although, generally the indentations 105 are particularly usefulin hollow golf clubs, such as metalwoods and utility club heads, theymay be used on any type of club head including irons, wedges andputters. The indentations may be used on any surface of the transitionzone 104, whether visible, such as on the exterior of the club head 101,or non-visible, such as on the interior of the club head 101.

As described above, if the club head is a wood type club head, it ispreferred that the inner cavity has a volume at least 115 cubiccentimeters, and more preferably at least 250 cubic centimeters, andmost preferably 350 cubic centimeters or more. Preferably, the mass ofthe inventive club head is greater than 150 grams but less than 300grams, more preferably greater than 170 g and less than 260 g, and mostpreferably greater than 185 g and less than 220 g. Further, part andmanufacturing details and additional test results regarding the CORvalues of inventive club heads are discussed in detail in the parentcase.

As shown in FIG. 16B, the indentation 105 may have an overall length l.Generally, the length l ranges from about 1 mm to about 20 mm. Ifmultiple indentations 105 are provided in the transition zone 104, theymay have the same or different lengths l. As shown in FIG. 16B, thedepth d of the indentation 105 may vary throughout its length l. Asshown in FIG. 17A, the depth d of the indentation 105 is defined as thegreatest depth of the indentation. The indentations 105 generally have adepth d of about 0.5 mm to about 2 mm. The indentations 105 may have adepth d that is about 5% to about 90% of the thickness t₁. Morepreferably, the depth d is about to 20% to 80% of the thickness t₁. Mostpreferably, the depth d is about 40% to 60% of the thickness t₁. Thedepth d of the indentations preferably gradually transitions to itsgreatest depth d. The indentations 105 also have a width w, defined asthe greatest width of the indentation, of about 0.5 mm to about 5 mm. Itwill be appreciated that the overall depths and widths of the indention105 may vary on the individual indentation and that the depths d andwidths w of the indentations 105 may vary relative to each other asshown in FIG. 17B. Additionally, when multiple indentations 105 areprovided in a transition zone 104, they may be spaced by distance salong their lengths. The spacing distance s is defined as the smallestdistance between adjacent indentations 105. The spacing distance sbetween the indentations 105 is generally between about 1 mm and 10 mm.The spacing distance s between the indentations 105 in a transition zone104 may be the same or may be varied. The indentations 105 may have anydesired shape, from circular to elliptical to polygonal. Preferably, theindentations 105 are elongated ellipses as shown in FIGS. 18-20. Asshown in FIGS. 17A-17B, the cross-sections of the indentations 105 mayhave a semicircular shape.

The size and number of the indentations 105 provided in the transitionzone 104 will determine the weight savings. The indentations 105 in thetransition zones 104 generally save from 0.5 g to 10 g, preferably from1-6 g. Preferably, the mass removed from the transition zone 104 is atleast about 0.5% of the mass of club head. More preferably, the massremoved is about 1% to about 10% of the mass of the club head. The massmay then be relocated to improve the playability characteristics of theclub head 101 as described further below. The transition zone 104 has amass. The mass removed from the transition zone 104 by the indentations105 is preferably at least 5% of the mass of the transition zone. Morepreferably, the mass removed from the transition zone is between 10 and40% of the mass of the transition zone 104.

As shown in FIG. 18, the transition zone 104 may be provided proximatethe face 106 of the club head 101. In particular, the transition zone104 is provided between the face 106 and the body 107 of the club head101. The transition zone 104 features multiple indentations 105. In thisembodiment, the indentations 105 may be provided on the toe sidetransition zone 108 of the club head between the face 106 and body 107of the club head 101 as shown, or may be provided on one or more of thetoe 108, heel 109, crown 110 or sole 111 transition zones between theface 106 and body 107 of the club head 101. It will be appreciated thatthe indentations 105 may extend onto the face 106 of the club headtoward the face insert 112. This embodiment, with the indentations 105provided on a toe transition zone 108, results in a weight savings of4-8 g. Placement of this mass toward the rear of the club head 101 movesthe center of gravity in the club head rearward by at least 1 mm. Itwill be appreciated that although this embodiment is shown on theinterior surface of the club head, that it could also be provided on theexterior surface of the club head.

As shown in FIG. 19, the transition zone 104 may be provided between thecrown 113 and the sole 114 of the club head 101. The transition zone 104features multiple indentations 105. In this embodiment, the indentations105 may be provided on the toe side 115 of the club head between thecrown 113 and sole 114 of the club head 101 as shown, or may be providedon one or more of the toe 115, heel 116 and rear 117 transition zonesbetween the crown and sole of the club head. This embodiment, with theindentations 105 provided on a toe transition zone 115, results in aweight savings of 3-6 g. Placement of this mass in the sole 114 of theclub head 101 moves the center of gravity in the club head below thecenter line of the club head by at least 1 mm. It will be appreciatedthat although this embodiment is shown on the interior surface of theclub head, that it could also be provided on the exterior surface of theclub head.

As shown in FIG. 20, the transition zone 104 may be provided on thehosel 118 of the club head 101 between the face 106 and the heel 119 ofthe club head 101. The transition zone features multiple indentations105. In this embodiment, the indentations 105 may be provided on theexterior surface 120 of the hosel within the club head 101 as shown, ormay be provided on one or more of the interior 121 and exterior surfaces120 of the hosel 118 as shown in FIGS. 21A and 21B. In the embodiment ofFIG. 20, with the indentations 105 provided on the exterior surface 120of the hosel 118 within the interior of the club head 101, results in aweight savings of 2-4 g. Placement of this mass toward the rear of theclub head 101 moves the center of gravity in the club head rearward byat least 1 mm.

The indentations 105 may be formed as part of the club head 101, such asby being part of the original tooling to form the club head. This mayinclude formation of the indentations during casting. Alternatively, theindentations may be formed post-process, for example by machining orchemical etching the indentations into the transition zone after formingeither the respective portion of the club head or the whole club head.

As discussed above, the size and number of the indentations 105 providedin the transition zone 104 will determine the weight savings. Theindentations 105 in the transition zones 104 generally save from 0.5 gto 10 g, preferably from 2-8 g. This weight savings may then be moved toa more desirable location in the club head 101, such as low and backwithin the club head 101 to improve playability characteristics, such ascenter of gravity, as described above, and moment of inertia. Forexample, as shown by the coordinate system shown in FIGS. 18-20, a clubhead 101 according to the present invention preferably has a moment ofinertia about the vertical axis through the center of gravity, I_(yy),of about 2500 g·cm² to about 6000 g·cm². Additionally, a club head 101according to the present invention preferably has a moment of inertiaabout the horizontal axis from heel to toe through the center ofgravity, I_(xx), of about 1500 g·cm² to about 5000 g·cm². A club head101 according to the present invention preferably has a moment ofinertia about the horizontal axis through the center of gravity fromfront to back of the club head, I_(zz), of about 1500 g·cm² to about6000 g·cm².

While various descriptions of the present invention are described above,it should be understood that the various features of each embodimentcould be used alone or in any combination thereof. Therefore, thisinvention is not to be limited to only the specifically preferredembodiments depicted herein. Further, it should be understood thatvariations and modifications within the spirit and scope of theinvention might occur to those skilled in the art to which the inventionpertains. For example, the transition zones may be made of a differentmaterial than the first and second portions. It will be appreciated thatthe club head may be made of any suitable metal or non-metal materials,such as those discussed above and any suitable combination thereof toconstruct the club head. Accordingly, all expedient modificationsreadily attainable by one versed in the art from the disclosure setforth herein that are within the scope and spirit of the presentinvention are to be included as further embodiments of the presentinvention. The scope of the present invention is accordingly defined asset forth in the appended claims.

We claim:
 1. A golf club head comprising: a first club portion having afirst thickness t₁; a second club portion having a second thickness t₂;a transition zone having a mass and connecting the first club portion tothe second club portion; and at least two indentations provided in thetransition zone, at least one of the indentations having a maximum depthd, where d is about 40% to about 60% of the first thickness t₁, whereinthe club head is hollow with a volume of at least 250 cubic centimetersand the indentations are provided on an interior nonvisible surface ofthe hollow portion of the club head, and wherein the indentations reducethe mass of the transition zone by at least 0.5%.
 2. The golf club headof claim 1, wherein the indentations reduce the mass of the transitionzone by about 10% to about 40%.
 3. The golf club head of claim 1,wherein the indentations reduce the mass of the transition zone withoutthe indentations by about 0.5 g to about 10 g.
 4. The golf club head ofclaim 3, wherein the indentations reduce the mass by about 2 g to about8 g.
 5. The golf club head of claim 3, wherein the maximum depth d isbetween about 0.5 mm to about 2 mm.
 6. The golf club head of claim 3,wherein the indentations have lengths ranging from about 1 mm to about20 mm and a maximum width w ranging from about 0.5 mm to about 5 mm. 7.The golf club head of claim 3, wherein a minimum spacing distance sbetween the indentations is about 1 mm to about 10 mm.
 8. The golf clubhead of claim 3, wherein the indentations are formed by machining orchemical etching.
 9. The golf club head of claim 3, wherein theindentations are formed by casting.
 10. The golf club head of claim 1,wherein the first portion of the club head is a crown portion of theclub head, the second portion of the club head is a sole portion of theclub head, and the transition zone is provided between the crown portionand the sole portion of the club head.
 11. The golf club head of claim10, wherein the center of gravity is provided below a horizontal centerline of the club head by at least 1 mm.
 12. The golf club head of claim1, wherein the transition zone is provided proximate a face insert ofthe club head.
 13. The golf club head of claim 12, wherein the firstportion of the club head is a face insert, the second portion of theclub head is a body of the club head, and the transition zone isprovided between the face insert and the body of the club head.
 14. Thegolf club head of claim 13, wherein the center of gravity is movedtoward a rear of the club head by at least 0.5 mm and lowered in theclub head by at least about 0.2 mm.
 15. The golf club head of claim 13,wherein the face insert is forged and the body of the club head is cast.16. The golf club head of claim 13, wherein the face insert furthercomprises: a central zone having a first flexural stiffness; and anintermediate zone concentric with the central zone, the intermediatezone having a second flexural stiffness, and wherein the first flexuralstiffness is higher than the second flexural stiffness.
 17. The golfclub head of claim 1, wherein the moment of inertia about the verticalaxis though the center of gravity of the club head, I_(yy), is about2500 g·cm² to about 6000 g·cm².
 18. The golf club head of claim 1,wherein the moment of inertia about the vertical axis though the centerof gravity of the club head, I_(xx), is about 1500 g·cm² to about 5000g·cm².
 19. The golf club head of claim 1, wherein the moment of inertiaabout the vertical axis though the center of gravity of the club head,I_(zz), is about 1500 g·cm² to about 6000 g·cm².
 20. The golf club headof claim 1, wherein the mass removed from the transition zone isthereafter provided in the perimeter of the club head.